One of the best-known physical properties of topaz is its hardness. It has a hardness of 8 on the Mohs hardness scale making it the hardest silicate mineral. It also serves as the Mohs hardness scale index mineral for a hardness of 8. Every student who takes a physical geology course learns about the hardness of topaz. Diamond, corundum, and chrysoberyl are the only commonly known minerals that are harder.

What Color is Topaz?

Topaz occurs in a wide range of natural colors; however, most natural topaz is colorless. The most highly regarded colors are the reds and pinks, which receive their color from trace amounts of chromium. Chromium is also responsible for the color in violet and purple topaz.

A variety known as "imperial topaz" is especially valuable because people enjoy its reddish orange to orangy red colors, which often both occur in the same crystal. Most of the world's imperial topaz is found in Brazil. Topaz with a natural blue color is very rare and valuable.

Yellow, brown, and colorless topaz have lower values. These colors are often heated, irradiated, coated, and treated in other ways to alter their color.

Use of Topaz as a Gemstone

The name "topaz" and many language variants have been used for yellowish gemstones for at least two thousand years. At that time yellowish gems were called "topaz" in many parts of the world. Many of the earliest gem traders did not realize that these yellowish stones were actually different materials.

Then, about two hundred years ago, people who traded in gems began to realize that these yellowish gems might be topaz, quartz, beryl, olivine, sapphire, or one of many other minerals. They also learned that topaz occurred in a wide range of colors other than yellow.

If you visited a jewelry store as recently as fifty years ago and asked to see topaz, you would likely have been shown gems that were in the color range of yellow, orange, and brown.

Starting in the 1970s and 1980s, the most common color that you would be shown began to be blue. This blue color was usually produced by treatments that converted colorless topaz into a more marketable gemstone.